Mosquito season in Monroe County, IL: when it starts and ends
Mosquito months in Monroe County
In a normal year mosquito season in Monroe County, IL starts around March 31 and ends around November 4, about 31 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Monroe County, and when
- Start tipping out standing water weekly by March 17.
- Book any yard treatment for late March, ahead of the July peak.
- Repellent can go away after November 4.
- 1 West Nile case since 2016 (last 2016): you should use repellent at dusk June to August, more so if over 60.
Monroe County against the rest of IL
Monroe County has the 14th longest season of 102 IL counties, at 218 days against 232 in Pulaski County and 174 in Boone County. Its mean temperature is 55.9°F.
- Perry County: March 28 to November 2 (219 days, 0 WNV)
- Clinton County: March 30 to November 3 (219 days, 2 WNV)
- Williamson County: March 29 to November 1 (217 days, 3 WNV)
- Jackson County: March 30 to November 1 (216 days, 3 WNV)
West Nile in Monroe County
From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Monroe County (2 neuroinvasive) across 3 years. The worst was 2016 with 1; the latest was 2016.
More: how the dates are worked out · when the season starts across the US.